LeetCode Top Interview 150

133. Clone Graph

Medium

Given a reference of a node in a connected undirected graph.

Return a deep copy (clone) of the graph.

Each node in the graph contains a value (int) and a list (List[Node]) of its neighbors.

class Node { public int val; public List neighbors; }

Test case format:

For simplicity, each node’s value is the same as the node’s index (1-indexed). For example, the first node with val == 1, the second node with val == 2, and so on. The graph is represented in the test case using an adjacency list.

An adjacency list is a collection of unordered lists used to represent a finite graph. Each list describes the set of neighbors of a node in the graph.

The given node will always be the first node with val = 1. You must return the copy of the given node as a reference to the cloned graph.

Example 1:

Input: adjList = [[2,4],[1,3],[2,4],[1,3]]

Output: [[2,4],[1,3],[2,4],[1,3]]

Explanation:

There are 4 nodes in the graph.
1st node (val = 1)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
2nd node (val = 2)'s neighbors are 1st node (val = 1) and 3rd node (val = 3).
3rd node (val = 3)'s neighbors are 2nd node (val = 2) and 4th node (val = 4).
4th node (val = 4)'s neighbors are 1st node (val = 1) and 3rd node (val = 3). 

Example 2:

Input: adjList = [[]]

Output: [[]]

Explanation: Note that the input contains one empty list. The graph consists of only one node with val = 1 and it does not have any neighbors.

Example 3:

Input: adjList = []

Output: []

Explanation: This an empty graph, it does not have any nodes.

Example 4:

Input: adjList = [[2],[1]]

Output: [[2],[1]]

Constraints:

• The number of nodes in the graph is in the range [0, 100].
• 1 <= Node.val <= 100
• Node.val is unique for each node.
• There are no repeated edges and no self-loops in the graph.
• The Graph is connected and all nodes can be visited starting from the given node.

Solution

from typing import Dict, List, Optional

class Node:
    def __init__(self, val=0, neighbors=None):
        self.val = val
        self.neighbors = neighbors if neighbors is not None else []

class Solution:
    def cloneGraph(self, node: Optional[Node]) -> Optional[Node]:
        return self._cloneGraph(node, {})

    def _cloneGraph(self, node: Optional[Node], processed_nodes: Dict[Node, Node]) -> Optional[Node]:
        if node is None:
            return None
        elif node in processed_nodes:
            return processed_nodes[node]
        new_node = Node()
        processed_nodes[node] = new_node
        new_node.val = node.val
        new_node.neighbors = []
        for neighbor in node.neighbors:
            cloned_neighbor = self._cloneGraph(neighbor, processed_nodes)
            if cloned_neighbor is not None:
                new_node.neighbors.append(cloned_neighbor)
        return new_node

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